Carbon black and silica have traditionally been used as fillers for reinforcing the physical and mechanical properties of elastomers, or rubbers selected from conjugated diene homopolymers and copolymers, copolymers of conjugated diene with vinyl monomers or terpolymers of diene with vinyl monomers, used to manufacture tires.
Silica has been used as a reinforcement material in tread compounds to reduce rolling resistance. See U.S. Pat. No. 5,227,425 to R. Rauline; U.S. Pat. No. 4,519,430 to S. Ahmad et al.; and, U.S. Pat. No. 3,873,489 to F. Thurn et al. However, conventionally compounded silica reinforced rubbers without coupling agents, such as 3,3'-bis(triethoxysilylpropyl)tetrasulfide, or 3-mercaptopropyltrimethoxysilane, have the disadvantage of exhibiting low modulus and reduced abrasion resistance, slow cure rates, and poor cure efficiency (i.e., extent of cross-linking achieved during curing or vulcanization) as compared to carbon black reinforced rubbers. See M. P. Wagner, Rubber Chemistry & Technology, vol. 49, pp. 703-773 (1976); and F. Thurn et al., U.S. Pat. No. 3,873,489. Increases in tensile and dynamic storage moduli are known to improve road handling and performance of tires. See S. Futamura and M. Engelhardt, Akron Rubber Group Meeting, Akron, Ohio, U.S.A., Jan. 23, 1986. Silica interferes with the sulfur cure process and leads to low rubber-filler interaction which is responsible for low modulus and poor abrasion.
The use of coupling agents, such as polyfunctional organosilanes, including 3,3'-bis(triethoxysilylpropyl)tetrasulfide (hereinafter referred to as TESPT) or 3-mercaptopropyltrimethoxysilane (hereinafter referred to as A-189) have conventionally been used to enhance modulus, and abrasion resistance of silica-reinforced rubbers. While M. P. Wagner, Rubber Chemistry & Technology, vol. 49, pp. 703-773 (1976), N. L. Hewitt, Rubber World, pp. 24-30 (June 1982), F. Thurn et al., U.S. Pat. No. 3,873,489, and S. Wolff, U.S. Pat. No. 4,229,333 teach the use of coupling agents, such as TESPT and A-189 in a special formulation to improve the modulus of silica-reinforced rubbers, the resulting rubber compositions, nevertheless, exhibit slow cure rates, low hardness and moduli.
Benzotriazole and tolyltriazole have been used as a coating for brass-coated steel belts used in tires to reduce their corrosion and enhance adhesion between the steel belt and the (belt) skim compound. EP Pub. No. 61,986 to Shemenski, et al., CA Pat. No. 1,162,674 to Korpics, et al., and U.S. Pat. No. 4,169,112 to Elmer, disclose the addition of triazole (not exceeding 3 parts per hundred of rubber) and cobalt salts to a carbon black reinforced skim compound to improve its adhesion to the brass plated steel cord, and also reduce corrosion of the steel cord. None of the references teach the inventive rubber compounds, nor compounds suitable for tread, undertread, tread cushion, bead, or sidewall tire components containing silica, and triazoles. In addition, Korpics, and Elmer do not teach the enhanced road performance and handling of tires, as indicated by improvement in dynamic modulus (S. Futamura et al., Akron Rubber Group Meeting, Akron, Ohio, U.S.A., Jan. 23, 1986) made with silica, and silica and carbon black-reinforced rubber compositions having triazoles. Moreover, Shemenski, Korpics, and Elmer do not teach improving cure rates and moduli of rubber components with triazole with little to no effect on hysteresis. Further, none of the references disclose improved hardness, abrasion resistance, tensile strength and increased cure efficiency. None of the references, moreover, teach the use of triazoles in tire compounds, especially in tread where silica is a reinforcing filler.
What is desired, therefore, is a silica-reinforced rubber compound having improved cure rates and high moduli, and exhibiting little to no change in hysteresis (as indicated by tan .delta. at 70.degree. C.), as compared to conventional silica and carbon black-reinforced rubber compounds. Also desired is a silica-reinforced rubber composition having high cure efficiency, improved hardness, abrasion resistance and durability. What is further desired is a tire with improved road performance and handling characteristics, as indicated by improvement in dynamic storage modulus (E') that is economical to produce as indicated by improved cure rate. What is even further desired is a method for improving road performance.